A bot is a program that runs on a computer 24/7, automating mundane tasks for the owner, even if the owner is not logged in. Bots are also used on the Internet in a variety of ways, for example on search engines.

Search engine bots, also called spiders and crawlers, explore the World Wide Web. For example, they retrieve Web pages and follow all of the hyperlinks within each. Once they have that information, they generate catalogs that can be accessed by search engines. Popular search sites, such as Google use this kind of automated method along with their own proprietary algorithms to generate their uniquely accurate search results. Webmasters are encouraged to understand the peculiarities of each search engine's bot so that they can design pages for retrieval by specific keywords.

Another online example is "shopping bots," accessible through a Web site's proprietary technology, these bots search the Web for the cheapest prices of products (such as clothing). There's also "gaming bots' and "mailbots" and much more. It's now broken down into "good bots" and "bad bots":

Good Bots:

Chatbots

Crawlers

Transactional bots

Informational bots

Entertainment / Art bots

Game bots

Monitoring bots

Backlink checker bots

Social Network bots

Partner bots

Aggregator / feedfetcher bots

Bad Bots:

Hackers

Spammers

Scrapers

Impersonators

Scalpers

Spam bots

Historical perspective: IRC bots are programs that connect to an IRC network and
interact with IRC in very much the same way a normal user does (in
fact, IRC servers treat bots as regular users). Most IRC bots
are used for channel control. Also known as "automatons," bots are
disliked by IRC operators and long-time IRC users because of the system
resources they consume.